Assembly adhesive based on an aqueous (co)polymer dispersion

ABSTRACT

An aqueous polymer adhesive is provided containing styrene polymers or styrene copolymers with alkyl acrylate acid/or alkyl methacrylates and a thickener system containing an inorganic thickener and an aqueous dispersion of an acrylic acid/acrylamide copolymer which can be partially replaced by a dispersion of a (co)polymer containing acrylate residues, a dispersion of a (co)polymer containing acrylic acid residues and methacrylic acid residues and polyarethanes. The adhesive has a high initial strength and can be in layers up to 30 mm thick.

RELATED APPLICATIONS

This application is a 35 U.S.C. 371(c) application of PCT/EP01/03627filed Mar. 30, 2001 which claims priority form German Application DE 10016 673.3 filed Apr. 4, 2000, the entire contents of each application areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to an adhesive based on an aqueous polymerdispersion containing added thickeners and optionally fillers, pigments,preservatives, solvents, plasticizers and other auxiliaries. Theinvention also relates to its production and to its use as an assemblyadhesive.

BACKGROUND OF THE INVENTION

An assembly adhesive is understood to be a composition which, on thestrength of the following properties, is suitable for assembly purposesabove all in the building industry:

very high early strength and ultimate strength in the bonding of wood,metals, ceramics, PVC and other plastics both indoors and outdoors andparticular abilities in regard to

gap bridging,

adhesion spectrum and

flexibility.

A preferred application for assembly adhesives is the rapid andpermanent fixing of objects to ceilings, walls and floors. A particularrequirement in this regard is the rapid and simple assembly of heavyobjects without any need for additional fixing after application of theadhesive (for example in the bonding of bricks, clinker bricks, panels,ceiling boards, etc.). The adhesive composition also has to be capableof “bridging” any surface unevenness (gap bridging).

The assembly adhesives hitherto available on the market have a maximumearly strength of 10 g/cm⁻² so that, although light objects can beassembled without any need for additional fixing, problems do arise inthe case of heavy objects, such as ceiling panels for example. Furtherproblems arise in the assembly of items which are under tension (forexample curved skirting boards). Items such as these have to beadditionally fixed until the adhesive has cured. Assembly applicationssuch as these always involve time-consuming and, in some cases,complicated extra work.

There are four types of assembly adhesives:

a) solvent-containing systems,

b) reactive systems,

c) hotmelt adhesives,

d) water-based systems.

Solvent-containing assembly adhesives are unpopular, particularly forindoor work involving large surface areas, because troublesome odoremission is often caused by solvent vapours. The advantage of usingsolvent-containing systems is that the solvent present is able to escapequickly from the adhesive composition so that high early strength can beobtained relatively quickly for assembly jobs.

Reactive systems and hotmelts either require specialconditions/equipment for application or take a relatively long time todevelop adequate adhesion properties for assembly work.

Water-based systems have the disadvantage that the water present isreleased very slowly. Accordingly, the curing process of the adhesive isrelatively slow. The major advantage of water-based systems is thatthere is no odor emission and/or health risk from solvent vapours.However, there have hitherto been no assembly adhesives with adhesionvalues in excess of 10 and more particularly in excess of 15 g/cm⁻².

Where acrylate dispersions are heavily thickened with relatively highconcentrations of acrylate thickeners to achieve high early strength(particularly via their viscosity), it has hitherto only been possibleto obtain very high-viscosity adhesive compositions that are difficultto apply, are not stable in storage and show poor wetting behavior onthe substrates to be bonded.

GB 2 061 990 describes an adhesive for fixing ceramic tiles. It contains

2 to 50% by weight of an aqueous dispersion or solution of an organicpolymer with a solids content of 30 to 70%,

4 to 80% by weight of an inorganic filler,

0.5 to 15% by weight of an organic additives and

0 to 10% by weight of auxiliaries.

In the Examples, adhesives are made up from the following components:

100 parts by weight of a styrene/acrylate copolymer in the form of adispersion with a solids content of 45%,

450 parts by weight of sand with various particle sizes,

5 parts by weight of a coalescence solvent based on an aromatic glycolether,

1 to 2 parts by weight of cellulose ether with a viscosity of 15,000 asthickener,

2 to 1 part by weight of Aerosil and

50 to 55 parts by weight of water.

Besides cellulose ethers, polyacrylates are mentioned as organicthickeners. The adhesive in question is said to be used for fixingceramic tiles to floors. Apparently, however, ceramic tiles can even befixed to walls. The disadvantage of this known adhesive is that itsearly strength is not high enough for fixing heavy items, such as tilesfor example, to walls immediately after levelling of the adhesive.

The problem addressed by the present invention was to provide a storableadhesive with very high early strength for fixing heavy items. Theadhesive would be easy to use. This would apply in particular to itsapplication to and spreading over the substrate.

BRIEF DESCRIPTION OF THE INVENTION

The solution provided by the invention is defined in the claims andconsists primarily in a composition that can be produced from thefollowing components:

A) 10 to 98, more particularly 51 to 88 and above all 60 to 70% byweight of at least one dispersion of a copolymer of at least styrene andan alkyl acrylate or alkyl methacrylate containing 1 to 12 and moreparticularly 2 to 8 carbon atoms in the alkyl group, the solids contentof the dispersion being in the range from 30 to 80% by weight and moreparticularly in the range from 40 to 65% by weight,

B) a thickener of a combination of

a) 0.4 to 6, more particularly 0.5 to 5 and above all 1 to 3% by weightof an inorganic thickener, such as highly disperse silica, and

b) 1 to 10 and more particularly 1.5 to 5% by weight of an aqueoussystem of a copolymer based on at least acrylic acid and acrylamide witha solids content of 10 to 40 and more particularly 25 to 35% by weight,up to 90% by weight and more particularly up to 50% by weight of thisaqueous system being replaceable by at least one of the followingaqueous polymer dispersions containing polymers based on acrylates,copolymers based on acrylic acid and methacrylic acid and water-solublepolyurethanes with a solids content of 20 to 40 and more particularly 25to 35% by weight,

C) 0 to 88 and more particularly 20 to 35% by weight of inorganic ororganic fillers, more particularly chalk, limestone powder, sand, marblepowder or titanium dioxide,

D) 0 to 2% by weight of inorganic or organic pigments, more particularlyiron oxides,

E) 0 to 3 and more particularly 0 to 1% by weight of auxiliaries, moreparticularly dispersion aids, such as Pignmentverteiler A (“PigmentDispersant A”) and preservatives,

F) 0 to 40 and more particularly 0 to 10% by weight of plasticizers and

G) water.

DETAILED DESCRIPTION OF THE INVENTION

The percentage by weight of styrene in the styrene/methacrylate orstyrene/acrylate copolymers should be in the range from 30 to 100% byweight and more particularly in the range from 50 to 100% by weight. Thestyrene comonomer may be substituted, for example by a methylsubstituent. The alkyl group of the acrylate may be linear, branched orcyclic and optionally substituted. Examples are methyl, ethyl,isopropyl, butyl, dodecyl, cyclohexyl, 2-ethylhexyl and 2-hydroxyethyl.The acrylates may also contain reactive groups for subsequentcrosslinking. Corresponding reactive groups may also contain vinylcomonomers, for example a silane group. The Si(Alk)₃ group may beattached to the vinyl group either directly or by a (CH₂)_(n) radicalwhere n may be a number of 2 to 6 and preferably has a value of 3 or 0.The alkyl groups may contain 1 to 4 carbon atoms and preferably 1 or 2carbon atoms. Other comonomers can be vinyl esters, maleic acid esters(again containing 1 to 12 and preferably 2 to 8 carbon atoms in thealcohol component), ethylene, acrylamide, acrylic acid, butadiene,acrylonitrile both individually and in the form of mixtures. Themolecular weight is above 100,000 g/mole. Commercially available styrenecopolymers are: Acronal 290 D, Scopacryl D 343, Ubatol VAF 1539, AcronalS 360 D, Scopacryl PAA D 8875, Acronal S 400, Acronal S 401, Styrofan A900, Rhodopas DS 913, Joncryl 678, Vinnapas LL 6010 and SAF 54, NeocrylA 621 (styrene/acrylate copolymer), Pliotec LS 1 (styrene/butylacrylate/methacrylic acid terpolymer), Mowilith DM 611, Mowilith DM 680,Styropor P 555 (pure styrene), Buna EM 2116, Styrolux 684 D, Rhodopas SB012, (styrene/butadiene copolymer), Novodur P2M, Synthomer VL 10286(styrene/butadiene/acrylonitrile terpolymer). DL 345 from Union Carbide,Rhodapas DS 910 from Rhone Poulenc, Revacryl 248 from Harco/Clariant andPrimal P 308 M from Rohm and Haas are particularly preferred. Mixturesof various styrene/acrylate copolymer dispersions may also be used.

The styrene copolymers may be produced by known methods, moreparticularly by emulsion or bead polymerization. These processes giveaqueous dispersions with a concentration of around 40 to 70% by weightof styrene copolymer. However, the styrene copolymers may also beproduced in bulk or solution.

The thickeners are generally high molecular weight substances whicheither absorb water and swell in the process or form intermolecularlattice structures. The organic thickeners ultimately change into aviscous, true or colloidal solution.

The organic thickener contains an aqueous system of a copolymer based onat least acrylic acid and acrylamide, preferably emulsified in an oilfraction, more particularly a petroleum fraction. However, it may alsoquite generally be an aqueous dispersion of the copolymer or an aqueoussolution. The solids content of the system is in the range from 10 to40% and more particularly in the range from 25 to 35%, as measured toDIN 53189 or ISO 1625. Its pH value as measured DIN ISO 976 is above allin the range from 7.5 to 9. Actual examples of the w/o emulsion areCollacral HP (BASF) and Texipol types (Scott-Bader).

The organic thickeners used as auxiliaries are aqueous dispersions orsolutions which may replace up to 90% by weight and more particularly upto 50% by weight of the aqueous system of the copolymer based on atleast acrylic acid and acrylamide, preferably the w/o emulsion. Actualexamples are

the water-soluble polyurethane thickener Nopco DSX 3290 (Cognis),

the aqueous solution of the terpolymer of acrylates and methacrylatesand carboxyfunctional comonomers Indunal T 112 (Indulor Chemie) which isan associative anionic thickener,

the acrylate polymer dispersion Acrysol TT 615 (Rohm & Haas) which is analkali-swellable anionic dispersion with a solids content of ca. 30% byweight,

polymer dispersion based on acrylic acid and acrylamide.

The function of the fillers is to reduce shrinkage and to influenceconsistency. Actual examples are in particular the Omyacarb chalks(Oyma).

Other suitable inorganic filler particles are, for example, fillerparticles of andalusite, sillimanite, kyanite, mullite, pyrophyllite,imogolite and allophane. Compounds based on sodium aluminates or calciumsilicates are also suitable, as are compounds based on sodium aluminatesor calcium silicates. Also suitable are minerals, such as silica,calcium sulfate (gypsum) which does not come from waste-gasdesulfurization plants in the form of anhydrite, semihydrate ordihydrate, silica flour, silica gel, barium sulfate, titanium dioxide,zeolites, leucite, potash feldspar, biotite, the group of soro-, cyclo-,ino-, phyllo- and tectosilicates, the group of poorly soluble sulfates,such as gypsum, anhydrite or heavy spar, and calcium minerals, such ascalcite or chalk (CaCO₃). The inorganic materials mentioned may be usedindividually. However, a mixture of two or more of the compoundsmentioned may equally well be used.

The filler particles have an ×50 value for the mean particle sizedistribution in the range from about 1 to about 120 μm, for example inthe range from about 3 to about 60 μm or in the range from about 60 toabout 90 μm, as measured with a Sympatec Helos H 0720 in isopropanol.

Organic filler particles which cannot readily be assigned to thewater-soluble or water-dispersible polymers are also suitable. Theseinclude in particular the finely ground plastic powders obtained in therecycling of plastics, more particularly the plastic powders obtainablefrom the fine grinding of highly crosslinked elastomeric or thermosetpolymers. One example of such powders is the rubber powder obtained, forexample, in the fine grinding of car tires.

The function of the pigments is to color the assembly adhesive. Organicpigments and iron oxides are preferred. Actual examples are theBayferrox types (Bayer).

Fatty compounds above all are used as plasticizers in a quantity of 0 to60% by weight, preferably in a quantity of 1 to 50% by weight and moreparticularly in a quantity of 10 to 40% by weight, based on thepolystyrene. Quantities of 0 to 40% by weight and more particularly 0 to10% by weight, based on the assembly adhesive, may also be used. Fattycompounds in the context of the invention are understood to be fattyacids, fatty alcohols or derivatives thereof, more particularlytriglycerides of higher fatty acids and preferably natural fats andoils. Full particulars can be found in WO 97/07173.

The auxiliaries include:

Preservatives for avoiding fungal and bacterial infestation. Actualpreservatives are JMAC-LP, 1%, a product of Johnson & Matthey, andMergal KM 3, a product of Troy Chemie GmbH.

Solvents for influencing open time and mechanical properties. An actualexample is butyl glycol.

Dispersion aids for improving the wetting behavior of the adhesives. Anactual example is Pigmentverteiler A (“Pigment Dispersant A”) (BASF).

A coalescing agent is not normally necessary.

Solvents do not have to be added either.

The balance to 100% by weight is water.

The pH value of the assembly adhesive is generally above 7 andpreferably in the range from 7 to 10. In this pH range, the thickeningeffect of the thickeners used is at its most favorable. At pH valuesabove 10, the acrylate thickeners used decompose and undergo a seriousdeterioration in their thickening effect. At pH values below 7, there isalso a marked deterioration in the thickening effect of the thickenersused.

The high early strength of the assembly adhesive used is largelyattributable to its particular rheology. In the so-called rest state,the assembly adhesive is dimensionally stable. During mechanicalprocessing, however, there is a reduction in viscosity so that theadhesive can readily be stirred and processed. Shearing causes areduction in viscosity so that, for example, the adhesive can readily beexpressed from a cartridge. When the shear forces are removed from theadhesive, it returns to its original viscosity. There is hardly anyevidence of a delayed increase in viscosity.

The assembly adhesive according to the invention is generally preparedas follows: all the components except the aqueous system of the acrylicacid/acrylamide copolymer are stirred for ca. 30 minutes at roomtemperature (ca. 20° C.) with a planetary stirrer comprising a dissolverdisk at a stirring speed of 50 r.p.m. and a dissolver speed of ca. 1,000r.p.m. to form an optically homogeneous composition. The aqueous systemof the acrylic acid/acrylamide polymer is then added and stirring iscontinued for another ca. 10 mins. Finally, a vacuum of ca. 10 mbar ispreferably applied for 5 mins. followed by venting. A creamy,spreadable, dimensionally stable composition is thus obtained by addingcomponent Bb) to the mixture of the other components.

Anyone can use the adhesive without any need for special equipment suchas, for example, hotmelt guns, UV lamps, or for complicated work suchas, for example, mixing components in certain ratios, applying primers,etc., as is the case with known assembly adhesives.

The assembly adhesive according to the invention is packed in cartridgesfrom which it can readily be expressed with a commercially availablegun. However, it may also be packed in buckets, tubes and pressurizedcontainers to TRG 300.

Accordingly, the present invention also relates to an adhesive thuspackaged, more particularly an adhesive in a cartridge.

By virtue of its creamy consistency, the adhesive levels easily afterapplication. It may be used for bonding, coating, sealing and fillingand, more particularly, for the bonding of constructions of wood,ceramic, glass, cement, metal and plastics.

The adhesive according to the invention may be applied in layerthicknesses of up to 30 mm and more particularly 1 to 20 mm.

The adhesive formulations according to the invention are distinguishedby the following features and are thus clearly distinguished from theperformance spectrum of other assembly adhesives based on aqueousdispersions, more particularly from the adhesive according to GB 2 061990:

1. The early strengths achieved with the described formulations are farabove the adhesion values hitherto known for dispersion-based assemblyadhesives. Tests on assembly adhesives based on polymer dispersionsproduced maximum early adhesion strengths of 10 g/cm⁻². By contrast, theformulations described above develop early adhesion values of more than10 and more particularly ≧15 g/cm⁻² or even ≧20 g/cm⁻².

2. The adhesive formulations described above show very pronouncedpseudoplastic behavior so that they are easy to process and easy tohandle. The extrusion rate as determined to ISO 9048 can vary withinwide limits according to the composition and is generally between 1,000and 7,000 and more particularly between 2,000 and 5,000 g/min at 23° C.for a nozzle diameter of 4 mm. Despite their very high viscosity, theformulations show good wetting behavior and, for example, can beexpressed from a cartridge with a normal cartridge gun. Nevertheless,not only are they dimensionally stable almost immediately, they are alsocapable of fixing even heavy objects without any aids.

3. Since the adhesive according to the invention is a dispersion-basedadhesive, no organic solvent vapors are emitted during drying of theadhesive so that drying is substantially odorless. In addition, there isno health risk from solvent vapors. The adhesive is thus particularlysuitable for indoor bonding involving large areas, especially since itsopen time can easily be varied and is generally up to 40 minutes andmore particularly up to 30 minutes.

4. Processing does not involve the use of special equipment, such as forexample the hotmelt guns used to apply hotmelts. Accordingly, thepresent invention also relates to the application of the adhesiveaccording to the invention from a cartridge. It may then readily bespread over the substrate, for example with a spatula.

5. The adhesive has a shelf life of more than 18 months on the basis ofthe unchanged ISO 9048 extrusion rate after storage for 6 months at 50°C.

The invention is illustrated by the following Examples.

I. Production of the Assembly Adhesive

An assembly adhesive was produced as described above from the followingcomponents (in % by weight):

1. Styrene/acrylate copolymer latex, 64.75 solids content ca. 50% byweight (Ucar-Latex-DL-345, Union Carbide) 2. Hydrophilic highly dispersesilica 2.0 (Kieselsäure-HDK-T-30, Wacker) 3. Acrylic acid/acrylamidecopolymer 2.0 aqueous solution emulsified in aliphatic petroleumfraction (Collacral-HP, BASF) 4. Marble, metamorphous (Omyacarb-5-GU,Omya) 29.9 5. Dispersion aid 1.0 polyacrylic acid ammonium salt(Pigmentverteiler A, BASF) 6. Silver chloride/titanium dioxidepreparation 0.05 in water/EtOH/anionic surfactants (JMAC-LP 1%, JohnsonMatthey) 7. Water It is characterized by the following properties: a)Early adhesion is between 28 g/cm⁻² and 30 g/cm⁻². b) The adhesive canbe expressed from a cartridge with a stand- ard cartridge gun (forexample Klapp Pistole DW 111 [Henkel] or DW 100 cartridge gun [Henkel]).c) Extrusion rate: 3,200 to 5,000 g/min as measured to DIN ISO 9048(pressure: 2 bar, temperature 23 ± 2° C., 50 ± 5% rel. air humidity,extrusion unit with an internal diameter of 5.0 cm, a length of 18 cmand a nozzle diameter of 4 mm). d) Open time: 15 to 25 mins. e) Density(Erichsen): 1.3 g/cm³.

II. Adhesive Properties

The adhesive properties of the adhesive according to the invention weredetermined by the following tests.

1. Method for Determining Early Adhesion

A marking line is applied to a 15×3 cm long test specimen of untreatedwood (beech plywood) with an 8 mm large hole in one side. The markingline is 10 cm from the 3 cm long side which does not have a hole.

A ca. 2 cm wide and 2 mm thick adhesive film is applied to the markedarea of 10×3 cm. Small balls 2 mm in diameter are then pressed into themiddle of the adhesive strip to guarantee the exact thickness of theadhesive film. The space between the balls is ca. 2 cm. The balls aresituated on an imaginary straight line in the middle of the appliedstrip of adhesive.

After the balls have been introduced into the adhesive layer, a 15×1.5cm aluminium rail (anodized aluminium) is pressed onto the balls. Thealuminium rail used has an 8 mm diameter hole on side. The rail isplaced on the adhesive layer in such a way that the hole does not lie inthe adhesive layer and the terminal edge of the rail is level with themarking line drawn in as described above.

For the measurement, the test specimen is suspended from a springbalance, the hook of the spring balance being engaged in the hole of thestrip of wood. The aluminium rail is then pulled slowly and uniformlyperpendicularly of the wooden strip until the rail begins to slide offthe adhesive layer. The value at which the rail begins to slide is readoff from the spring balance. The measured value represents the earlyadhesion for an area of 15 cm². If the value obtained is divided by 15,an adhesion value in g/cm² is obtained.

2. Results

An adhesion value of 30 g/cm² was obtained. This is sufficient forimmediately fixing a 11×21 cm building brick weighing 3.4 kg to avertical wall for a layer thickness of up to ca. 5 mm.

We claim:
 1. An aqueous polymer dispersion adhesive which comprises: A)10 to 98% by weight of at least one aqueous dispersion of a (co)polymercomprising residues of at least styrene and optionally at least onemember selected from the group consisting of alkyl acrylate and alkylmethacrylate containing 1 to 12 carbon atoms in the alkyl group, thesolids content of the dispersion being in the range from 30 to 80% byweight; B) a thickener comprising a combination of a) 0.4 to 6% byweight, based on the weight of the adhesive, of an inorganic thickener,and b) 1 to 10% by weight, based on the weight of the adhesive, of anaqueous system comprising a polymer comprising residues of at leastacrylic acid and acrylamide with a solids content of 10 to 40% byweight, wherein up to 90% by weight of the aqueous system beingreplaceable by at least one polymer dispersion selected from the groupconsisting of polymer dispersions containing acrylate residues,copolymer dispersions containing at least acrylic acid residues andmethacrylic acid residues and polyurethanes the aqueous system having asolids content of 20 to 40% by weight; C) 0 to 88% by weight of fillers;D) 0to 2% by weight of pigments; E) 0 to 3% by weight of auxiliaries; F)0 to 40% by weight of plasticizers; and G) water.
 2. The adhesive asclaimed in claim 1 comprising: A) 51 to 98% by weight of thestyrene/acrylate (co) polymer dispersion; B) a) 1 to 3% by weight ofhighly disperse silica, c) 1 to 5% by weight of an acrylicacid/acrylamide copolymer w/o emulsion.
 3. The adhesive as claimed inclaim 1, having a pH value greater than
 7. 4. The process for theproduction of the adhesive of claim 2 which comprises: forming a mixtureof A) with the inorganic thickener and any of C) through G) to beincluded in the composition, and as a final step admixing the aqueoussystem of the copolymer comprising at least acrylic acid and acrylamideresidues with the mixture.
 5. The method of applying the adhesive ofclaim 2 wherein the adhesive is applied from a cartridge.
 6. The methodof claim 5 wherein the adhesive is applied to the substrate in a layerthickness of up to 30 mm.
 7. The adhesive of claim 1 having a pH valuein a range of 7-10.
 8. The adhesive of claim 2 having a pH value ofgreater than
 7. 9. The adhesive of claim 2 having a pH value in a rangeof 7-10.
 10. The process for the production of the adhesive of claim 8which comprises: forming a mixture of A) with the inorganic thickenerand any of C) through G) to be included in the composition, and as afinal step admixing the aqueous system of the copolymer comprising atleast acrylic acid and acrylamide residues with the mixture.
 11. Themethod for applying the adhesive of claim 2 wherein the adhesive isapplied from a cartridge.
 12. The method for applying the adhesive ofclaim 3 wherein the adhesive is applied from a cartridge.
 13. The methodof claim 11 wherein the adhesive is applied to the substrate in a layerthickness of up to 30 mm.
 14. The method of claim 12 wherein theadhesive is applied to the substrate in a layer thickness of up to 30mm.
 15. The adhesive of claim 1 wherein the (co)polymer of styrenecontains 30% to 100% by weight of styrene residues.
 16. The adhesive ofclaim 2 wherein the (co)polymer of styrene contain from 30% to 100% byweight of styrene residues.
 17. The adhesive of claim 3 wherein the(co)polymer of styrene contains from 30% to 100% by weight of styreneresidues.